Why the Same Degree Arrives at Two Different Times
The fence explained why a body reads a different degree in the two frames. This page is about the consequence, and the consequence is larger than anyone expects.
A body is not a fixed dot. It is travelling along the fence. So if the two frames disagree about which degree it is at, they necessarily disagree about when it reaches any given degree.
The experiment
Aquila's Hotspot Transits study is the cleanest way to see this, because you choose the degree yourself. Give it a body, give it a degree between 0 and 360, and it reports the moment the body crosses it.
Then change one dropdown. Same body, same degree, same date range, Ref. Plane moved from Ecliptic to Equatorial. Everything else held still.
Here is what comes back. The times are local to the study's location, a New York one — the Sun's row is the 2025 equinox, 09:01 UT.
| Body | Degree | Ecliptic latitude | Ecliptic crossing | Equatorial crossing | Difference |
|---|---|---|---|---|---|
| Sun | 0° | −0.0002° | 2025-03-20 05:01:28 | 2025-03-20 05:01:21 | 7 seconds |
| Moon | 0° | +5.23° | 2030-01-09 14:46:38 | 2030-01-09 19:11:10 | 4h 25m |
| Mercury | 0° | −2.59° | 2026-04-14 23:21:29 | 2026-04-14 04:10:41 | 19 hours |
| Pluto | 180° | +15.65° | 1971-10-05 | 1968-10-04 | 3 years |
Those are real runs, not estimates. Pluto reaches 0° Libra in the autumn of 1971 by one measurement and the autumn of 1968 by the other.
The Sun is the control
Look at the first row before anything else.
The Sun's ecliptic latitude is two ten-thousandths of a degree — zero, to any precision that matters. And its two crossings agree to within seven seconds, which is the residue of a body that is very nearly but not exactly on the ecliptic.
That row is what makes the rest provable rather than merely asserted. If the difference were an artefact — a rounding error, a bug, a units mix-up — it would show up for the Sun as well. It does not. The effect appears exactly when the body has latitude, and in proportion to it.
This is the fence, doing what the fence said it would. The Sun is lying on the fence. Tilting a fence about its hinge does not move something that is lying on the hinge.
Why the Moon is beaten by Mercury
The third row looks wrong at first. Mercury has half the Moon's latitude and four times the time difference.
The reason is that a time difference is an angular offset divided by a speed. Both bodies are displaced along the fence by roughly four-tenths of their latitude — about 2.1° for the Moon and 1.0° for Mercury — but the Moon covers its 2.1° in four hours, while Mercury needs the better part of a day to cover 1.0°.
Angular offset comes from latitude. Time difference comes from offset divided by speed.
Which is why the slow outer bodies are so extreme. Pluto's 15.65° of latitude displaces it by about 6° along the fence, and Pluto takes years to cover 6°.
The one that proves it
Now the result that settles the mechanism beyond argument.
Run Pluto again at 270° instead of 180°, still carrying 6.28° of latitude:
| Body | Degree | Ecliptic latitude | Ecliptic crossing | Equatorial crossing | Difference |
|---|---|---|---|---|---|
| Pluto | 270° | +6.28° | 2008-01-25 21:38:04 | 2008-01-25 21:38:04 | none at all |
Identical to the second. A body well off the ecliptic, and the two frames agree perfectly.
The fence explains it in one line. 270° is as far from the hinge as it is possible to get. Out there the tilt lifts a hovering body straight up and down rather than swinging it sideways, so it stays over the same paling however high it is hovering. The same holds at 90°.
So the picture is complete, and it is entirely about position relative to the hinge:
| Where the body is | Effect of switching plane |
|---|---|
| On the ecliptic, at 0° or 180° | none — it is on the hinge |
| On the ecliptic, at 90° or 270° | none |
| On the ecliptic, in between | up to 2.5°, greatest near 45° |
| Off the ecliptic, at 0° or 180° | greatest — about 0.4 × latitude |
| Off the ecliptic, at 90° or 270° | none, at any latitude |
| Off the ecliptic, in between | both effects together |
A wrinkle worth knowing about the Moon
The Moon's row used 2030 rather than a nearer year, and there is a reason.
The Moon's latitude at any particular degree of longitude depends on where its nodes are, and the nodes travel right round the ecliptic every 18.6 years. In 2025 a node sat close to 0° Aries, so the Moon crossed that degree almost flat — and the two planes agreed to about ten minutes. By 2030 the node has moved, the Moon crosses 0° with better than 5° of latitude, and the gap has opened to four and a half hours.
The same body, the same degree, and a difference that varies by a factor of twenty-five depending on the year. Nothing is wrong with either figure.
What this means in practice
Neither answer is wrong. They are answers to different questions. When did Pluto reach 180° of celestial longitude? and when did Pluto reach 180° of right ascension? are not the same question, and there is no reason they should have the same answer.
A result is incomplete without its plane. A transit date carries an implicit frame, and for a slow high-latitude body that frame is worth years. Two studies compared across sessions must have had the same Ref. Plane setting or they are not comparable.
The default is Ecliptic, which is what tradition, every ephemeris, and every other astrological program mean by a transit. If you did not deliberately change the setting, your dates are ecliptic dates and they agree with everyone else's.
What comes next
The equatorial runs above reported plain degrees and no sign names — no
00°Lib00' anywhere in that output, where the ecliptic runs had it on every row.
That is deliberate, and it follows from everything on this page.